**Steps to replicate the issue** (include links if applicable):
* set up a MediaWiki instance (used MediaWiki docker)
* upload a video file through Special:Upload (used copy of [[:File:Caminandes_3_-_Llamigos_-_Blender_Animated_Short.webm]] from Commons, confirmed with another random .ogv file)
**What happens?**:
This warning:
```
Warning: Stats: stop() called before start() for metric 'media_thumbnail_generate_transform_seconds' in /var/www/html/w/includes/libs/Stats/Metrics/TimingMetric.php on line 80
```
appears on output on the File: page immediately after upload, and in the error log; otherwise nothing seems untoward.
It's possible that something in the core MediaHandler classes does something different from TimedMediaHandler and something isn't getting called in a base class that should, but I can't identify any instances of the string "media_thumbnail_generate_transform_seconds" in core except for the line that triggers the call that gives this warning, in MediaHandlerState::generateAndSaveThumb:
```
$timer = $statsFactory->getTiming( 'media_thumbnail_generate_transform_seconds' )
->copyToStatsdAt( 'media.thumbnail.generate.transform' );
$timer->start();
```
So why is it warning? What's producing this stat for other images? Is it being run by some external system that's set up for other file types in the Docker config?
**What should have happened instead?**:
No warnings should display. If the warning indicated a problem, that problem should be fixed.
**Software version** (on `Special:Version` page; skip for WMF-hosted wikis like Wikipedia):
git master
**Other information** (browser name/version, screenshots, etc.):
{F55447130}